Radio-frequency (RF) identification is the use of a wireless system that uses radio-frequency electromagnetic fields to transfer data from a transponder (e.g., a tag) to a reader, for the purposes of identification and tracking. The transponder contains electronically stored information that can be read by a reader base station of the reader within a read distance. Some passive transponders (e.g., with no battery) are powered and read within the read distance via magnetic fields (e.g., electromagnetic induction) from the reader base station.
For example, a backscattering method for a transponder within a key of a car together with a reader base station in the car (e.g., at a lock of the car), is a widely used method for immobilization used as anti-theft control of cars (e.g., immobilizer function of cars). The reader base station interacts, via an antenna, with the transponder and gets a backscattered signal including information from the transponder. However, due to high electromagnetic interference (EMI) on wires between the reader base station and a reader coil in the car, the reader base station has a low sensitivity, which limits the read distance between the transponder and the reader coil. Additionally down mixing of thermal and harmonics noises lead to low EMI immunity as well as low sensitivity and low read distance.
To solve these problems, in some cases, a separate reader coil exclusively is used for the immobilizer function and a separate electronic module is placed very close to the reader coil. In some cases, the reader base station is placed very close to the reader coil so that the transponder is mechanically very close to the reader coil (e.g., by putting the reader coil around the lock and placing the transponder into the key at a position very close to the reader coil). However, this solution involves high cost and reduced mechanical flexibility for the key design. Due to LC tolerances in the transponder and the reader coil, the backscattered signal can be zero amplitude modulation (e.g., pure phase modulation). Zero amplitude modulation can make it difficult to demodulate the backscattered signal to retrieve the transponder information for immobilization and/or identification.